1. Field of the Invention
The present invention relates to a method for preparing acrolein or methacrolein which comprises subjecting propylene, secondary propanol, isobutylene or tertiary butanol to gas phase catalytic oxidation with molecular oxygen.
2. Prior Art
Heretofore, there have been a variety of catalysts used in the preparation of acrolein or methacrolein through gas phase catalytic oxidation of propylene, secondary propanol, isobutylene or tertiary butanol with molecular oxygen. In particular, it has been known that catalysts which comprise, as essential components, Mo, Bi and Fe as well as at least one member selected from the group consisting of Ni and Co, and at least one member selected from the group consisting of K, Rb, Cs and Tl are effective for the aforementioned reaction and there have been proposed various such catalysts. For instance, in Japanese Unexamined Patent Publication (hereinafter referred to as "J.P. KOKAI") No. Sho 48-52713, a catalytic composition represented by the following general formula: EQU Co.sub.a Fe.sub.b Bi.sub.c L.sub.d H.sub.e Mo.sub.f O.sub.g
wherein L represents an element selected from the group consisting of P, As and B; H represents an element selected from the group consisting of K, Rb and Cs; and when f is assumed to be 12, a ranges from 2 to 15, b from 0.5 to 7, c from 0.1 to 4, d from 0 to 2, e from 0.01 to 1.0 and g is a value determined on the basis of the standard valencies of these constituent elements and calcined at a high temperature ranging from 650.degree. C. to 1,000.degree. C., is used as a catalyst for the gas phase catalytic oxidation reaction. If the catalyst is calcined at a high temperature of 650.degree. C. or higher, the selectivity to end products would be enhanced, but the problem of a decrease in the catalytic activity arises. GB Pat. No. 1529384 discloses method in which two types of catalyst are employed, one of which comprises a coating catalyst obtained by attaching to an inert carrier a catalytic component represented by the following general formula: EQU A.sub.a B.sub.b Fe.sub.c Bi.sub.d Mo.sub.12 O.sub.x
wherein A represents an alkali metal, an alkaline earth metal, Sm, Ta, Tl, In, Ga, B, P, As, Sb or mixture thereof; B represents Ni, Co, Mg, Mn or mixture thereof; a=0.about.8, b=0.about.20, c=0.1.about.10, d=0.01.about.6 and x is the number of oxygen atoms required for satisfying the valency requirement of the constituent elements and the other of which is the second catalyst comprising the aforementioned catalytic component per se, and the patent also discloses that the temperature control of an exothermic reaction at an industrially effective high feed rate can be ensured only by arranging this catalytic system in a tube of a fixed bed reactor so that a reactant is first brought into contact with the first catalyst and then with the second catalyst. The patent further states that when a conventional compression-molded catalyst comprising the foregoing catalytic component per se is employed, the heat generation is too large to control the reaction. Furthermore, U.S. Pat. No. 4,511,671 discloses, as a catalyst for use in preparing methacrolein, a ring-like catalyst which comprises a catalytically active substance represented by the following general formula: EQU Mo.sub.a W.sub.b Bi.sub.c Fe.sub.d A.sub.e B.sub.f C.sub.g D.sub.h O.sub.x
wherein A is a member selected from the group consisting of Ni and Co; B is a member selected from the group consisting of alkali metals, alkaline earth metals and thallium; C is a member selected from the group consisting of P, Te, Sb, Sn, Ce, Pb, Nb, Mn and Zn; D is a member selected from the group consisting of Si, Al, Ti and Zr; when a is assumed to be 12, b=0.about.10, c=0.1.about.10, d=0.1.about.20, e=2.about.20, f=0.about.10 , g=0.about.4, h=0.about.30, and x is determined by the oxidized conditions of the constituent elements and also discloses that the usual catalysts in the form of tablets show reduction in their activity upon using over a long time period and thus suffer from a problem of the stability thereof.
As has been discussed above, the conventional catalysts are insufficient in catalyst properties such as activity, selectivity, stability and duration of life and hence there has been desired for the improvement of these catalyst in such properties. Moreover, the methods for preparing these catalysts are insufficient in reproducibility since the quality of the resulting catalysts differs from lot to lot and thus the improvement of these catalyst has also been desired from this standpoint.